Light emitting device having vertical structure and method for manufacturing the same

ABSTRACT

A light emitting device having a vertical structure and a method for manufacturing the same, which are capable of increasing light extraction efficiency, are disclosed. The method includes forming a light extraction layer on a substrate, forming a plurality of semiconductor layers on the light extraction layer, forming a first electrode on the semiconductor layers, forming a support layer on the first electrode, removing the substrate, and forming a second electrode on a surface from which the substrate is removed.

This application is a continuation of prior U.S. patent application Ser.No. 11/704,390 filed Feb. 9, 2007 now U.S. Pat. No. 7,687,811, whichclaims priority to Korean Patent Application Nos. 10-2006-0025691, filedMar. 21, 2006 and 10-2006-0025692, filed Mar. 21, 2006 all of which areincorporated by reference for all purposes as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light emitting device having avertical structure, and more particularly, to a light emitting devicehaving a vertical structure and a method for manufacturing the samewhich are capable of increasing light extraction efficiency.

2. Discussion of the Related Art

Light emitting diodes (LEDs) are well known as a semiconductor lightemitting device which converts current to light, to emit light. Since ared LED using GaAsP compound semiconductor was commercially available in1962, it has been used, together with a GaP:N-based green LED, as alight source in electronic apparatuses, for image display.

The wavelength of light emitted from such an LED depends on thesemiconductor material used to fabricate the LED. This is because thewavelength of the emitted light depends on the band gap of thesemiconductor material representing energy difference betweenvalence-band electrons and conduction-band electrons.

Gallium nitride (GaN) compound semiconductor has been highlighted in thefield of high-power electronic devices because it exhibits a highthermal stability and a wide band gap of 0.8 to 6.2 eV. One of thereasons why GaN compound semiconductor has been highlighted is that itis possible to fabricate a semiconductor layer capable of emittinggreen, blue, or white light, using GaN in combination with otherelements, for example, indium (In), aluminum (Al), etc.

Thus, it is possible to adjust the wavelength of light to be emitted,using GaN in combination with other appropriate elements. Accordingly,where GaN is used, it is possible to appropriately determine thematerials of a desired LED in accordance with the characteristics of theapparatus to which the LED is applied. For example, it is possible tofabricate a blue LED useful for optical recording or a white LED toreplace a glow lamp.

On the other hand, initially-developed green LEDs were fabricated usingGaP. Since GaP is an indirect transition material causing degradation inefficiency, the green LEDs fabricated using this material cannotpractically produce light of pure green. By virtue of the recent successof growth of an InGaN thin film, however, it has been possible tofabricate a high-luminescent green LED.

By virtue of the above-mentioned advantages and other advantages ofGaN-based LEDs, the GaN-based LED market has rapidly grown. Also,techniques associated with GaN-based electro-optic devices have rapidlydeveloped since the GaN-based LEDs became commercially available in1994.

GaN-based LEDs have been developed to exhibit light emission efficiencysuperior over that of glow lamps. Currently, the efficiency of GaN-basedLEDs is substantially equal to that of fluorescent lamps. Thus, it isexpected that the GaN-based LED market will grow significantly.

Despite the rapid advancement in technologies of GaN-based semiconductordevices, the fabrication of GaN-based devices suffers from a greatdisadvantage of high-production costs. This disadvantage is closelyrelated to difficulties associated with growing of a GaN thin film(epitaxial layer) and subsequent cutting of finished GaN-based devices.

Such a GaN-based device is generally fabricated on a sapphire (Al₂O₃)substrate. This is because a sapphire wafer is commercially available ina size suited for the mass production of GaN-based devices, supports GaNepitaxial growth with a relatively high quality, and exhibits a highprocessability in a wide range of temperatures.

Further, sapphire is chemically and thermally stable, and has ahigh-melting point enabling implementation of a high-temperaturemanufacturing process. Also, sapphire has a high bonding energy (122.4Kcal/mole) and a high dielectric constant. In terms of a chemicalstructure, the sapphire is a crystalline aluminum oxide (Al₂O₃).

Meanwhile, since sapphire is an insulating material, available LEDdevices manufactured using a sapphire substrate (or other insulatingsubstrates) are practically limited to a lateral or vertical structure.

FIG. 1 shows a structure of an LED device having a lateral structure ofthe aforesaid general GaN-based LEDs.

A lateral type LED device includes an n-type GaN layer 2 formed on asapphire substrate 1, an active layer 3 (light emitting layer) formed onthe n-type GaN layer 2, and a p-type GaN layer 4 formed on the activelayer 3. An n-type electrode 5 is formed on a surface of the n-type GaNlayer 2, from which the active layer 3 is removed. A p-type electrode 6is formed on the p-type GaN layer 4.

Recent researches in the GaN-based semiconductor light emitting devicesare focused on the increase of luminance. Methods for increasingluminance of the light emitting devices include a method for improvinginternal quantum efficiency and a method for improving light extractionefficiency. Recently, researches in the method for improving the lightextraction efficiency have been actively proceeded.

The representative methods for increasing the light extractionefficiency include a method of etching the sapphire substrate with aregular pattern, roughening a surface of the p-type GaN layer, andforming a photonic crystal with a constant period by etching the p-typeGaN layer.

At present, the methods of etching the sapphire substrate and rougheningthe surface of the p-type GaN layer are applied to the mass productiontechnologies of the light emitting devices. The method using thephotonic crystal has been theoretically well known and studied throughlaboratorially simulated experiment. However, the method using thephotonic crystal is not applied to the mass production technologies ofthe light emitting devices until now.

The method using the photonic crystal has superior light extractionefficiency to the methods of etching the sapphire substrate androughening the surface of the p-type GaN layer.

As shown in FIG. 2, the representative method using the photonic crystalis to form a photonic crystal 7 by etching the p-type GaN layer 4 with aconstant periodical pattern in the basic structure of the LED devicedepicted in FIG. 1.

However, this method has a limitation in the improvement of the lightextraction efficiency, because of basically low electrical features ofthe p-type GaN layer 4, a thin thickness and degradation of theelectrical features by the etching.

Another method is to use a structure that the p-type GaN layer is grownon the substrate, the light emitting layer is grown on the p-type GaNlayer 2 and the n-type GaN layer is grown on the light emitting layer,and to form a photonic crystal structure on the n-type GaN layer.

However, basically low electric conductivity of the p-type GaN layer,low crystalline quality and degradation of electrical features by theetching make the growth of the p-type GaN layer on the substrateimpossible.

Another method is to grow the n-type GaN layer on the sapphiresubstrate, to subsequently grow the light emitting layer and the p-typeGaN layer, and then to grow the n-type GaN layer again. This method isto use electric tunnel junction characteristics between the p-type GaNlayer and the n-type GaN layer.

However, because of low electrical features of the p-type GaN layer,this method also has problem that resistance at a junction portion isincreased and resultantly operating voltage of the device is increased.

Yet another method is to sequentially grow the n-type GaN layer, thelight emitting layer and the p-type GaN layer over the sapphiresubstrate, to bond a reflective layer and a metal plate having a goodheat dissipating effect, and to form the photonic crystal by etching theexposed surface of the n-type GaN layer, from which the sapphiresubstrate is removed.

However, because the metal plate is not stable sufficiently in theetching process of the thin film layer, it is difficult to perform theetching process, and productivity is low.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a light emittingdevice having a vertical structure and a method for manufacturing thesame that substantially obviate one or more problems due to limitationsand disadvantages of the related art.

An object of the present invention is to provide a light emitting devicehaving a vertical structure and a method for manufacturing the samewhich can achieve a high-brightness and high-efficient light emittingdevice by adapting a photonic crystal structure capable of improvinglight extraction efficiency to the light emitting device.

Another object of the present invention is to provide a light emittingdevice having a vertical structure and a method for manufacturing thesame which can improve crystalline quality of a thin film by growing thethin film selectively on a light extraction structure formed in aspecific shape.

Yet another object of the present invention is to provide a lightemitting device having a vertical structure and a method formanufacturing the same which can improve efficiency of a light emittingdevice by controlling strain in a thin film.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To achieve the object and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein, amethod for manufacturing a light emitting device having a verticalstructure comprises: forming a light extraction layer on a substrate;forming a plurality of semiconductor layers on the light extractionlayer; forming a first electrode on the semiconductor layers; forming asupport layer on the first electrode; removing the substrate; andforming a second electrode on a surface from which the substrate isremoved.

In another aspect of the present invention, a light emitting devicehaving a vertical structure comprises: a support layer; a firstelectrode disposed on the support layer; a plurality of semiconductorlayers disposed on the first electrode; a photonic crystal layerdisposed on the semiconductor layers, the photonic crystal layer beingformed by a plurality of holes arranged periodically; and a secondelectrode disposed on the photonic crystal layer.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 is a sectional view illustrating an example of a conventionallight emitting device having a lateral structure;

FIG. 2 is a sectional view illustrating an example of a conventionallight emitting device having a lateral structure, at which a photoniccrystal is formed;

FIGS. 3 to 8 are sectional views illustrating a method for manufacturinga light emitting device having a vertical structure in accordance with afirst embodiment of the present invention, in which:

FIG. 3 is a sectional view illustrating a process of forming asemiconductor layer on a substrate;

FIG. 4 is a sectional view illustrating a process of forming a photoniccrystal on a semiconductor layer;

FIG. 5 is a plan view of FIG. 4;

FIG. 6 is a sectional view illustrating a process of filling dielectricmaterial in photonic crystal;

FIG. 7 is a sectional view illustrating a process of forming a pluralityof semiconductor layers on a photonic crystal structure; and

FIG. 8 is a sectional view illustrating a process of forming anelectrode and a support layer on semiconductor layers;

FIG. 9 is a sectional view illustrating an exemplary embodiment of alight emitting device having a vertical structure in accordance with thepresent invention;

FIGS. 10 to 12 are sectional views illustrating a method formanufacturing a light emitting device having a vertical structure inaccordance with a second embodiment of the present invention, in which:

FIG. 10 is a sectional view illustrating a substrate;

FIG. 11 is a sectional view illustrating a process of forming columns ofdielectric material on a substrate; and

FIG. 12 is a plan view of FIG. 11;

FIGS. 13 to 17 are sectional views illustrating a method formanufacturing a light emitting device having a vertical structure inaccordance with a third embodiment of the present invention, in which:

FIG. 13 is a sectional view illustrating a process of forming asemiconductor thin film on a substrate;

FIG. 14 is a sectional view illustrating a process of forming columns ofdielectric material on a semiconductor thin film;

FIG. 15 is a plan view of FIG. 14;

FIG. 16 is a sectional view illustrating a process of forming aplurality of semiconductor layers on columns of dielectric material; and

FIG. 17 is a sectional view illustrating a process of forming a firstelectrode and a support layer on semiconductor layers; and

FIG. 18 is a sectional view illustrating another exemplary embodiment ofa light emitting device having a vertical structure in accordance withthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings.

The present invention may, however, be embodied in many alternate formsand should not be construed as limited to the embodiments set forthherein. Accordingly, while the invention is susceptible to variousmodifications and alternative forms, specific embodiments thereof areshown by way of example in the drawings and will herein be described indetail. It should be understood, however, that there is no intent tolimit the invention to the particular forms disclosed, but on thecontrary, the invention is to cover all modifications, equivalents, andalternatives falling within the spirit and scope of the invention asdefined by the claims.

Like reference numbers refer to like elements throughout the descriptionof the figures. In the drawings, the thickness of layers and regions areexaggerated for clarity.

It will be understood that when an element such as a layer, region orsubstrate is referred to as being “on” another element, it can bedirectly on the other element or intervening elements may also bepresent. It will also be understood that if part of an element, such asa surface, is referred to as “inner”, it is farther from the outside ofthe device than other parts of the element.

In addition, relative terms, such as “beneath” and “overlies”, may beused herein to describe one layer's or region's relationship to anotherlayer or region as illustrated in the figures.

It will be understood that these terms are intended to encompassdifferent orientations of the device in addition to the orientationdepicted in the figures. Finally, the term “directly” means that thereare no intervening elements. As used herein, the term “and/or” includesany and all combinations of one or more of the associated listed items.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, components, regions, layersand/or sections, these elements, components, regions, layers and/orsections should not be limited by these terms.

These terms are only used to distinguish one region, layer or sectionfrom another region, layer or section. Thus, a first region, layer orsection discussed below could be termed a second region, layer orsection, and similarly, a second region, layer or section may be termeda first region, layer or section without departing from the teachings ofthe present invention.

<First Embodiment>

Hereinafter, a first embodiment of the present invention will bedescribed with reference to FIGS. 3 to 8.

In order to form a light extraction layer on a substrate, as shown inFIG. 3, a substrate 10 is subjected to surface treatment through a wettreatment process or a dry treatment process, and a GaN semiconductorlayer 20 is formed on the substrate 10 by using a common semiconductorthin film growing device.

The substrate 10 may be made of material selected from the groupconsisting of sapphire, silicon (Si), zinc oxide (ZnO), silicon carbide(SiC), and a combination thereof. Preferably, the GaN semiconductorlayer 20 is grown to a thickness of 0.3 to 5 μm. The GaN semiconductorlayer 20 may be formed using n-type GaN material.

As shown in FIG. 4, holes 21 with regular period and pattern are formedon the GaN semiconductor layer 20 by using a patterning process and anetching process. The planar shape of the substrate 10 and the GaNsemiconductor layer 20 with holes 21 is as that depicted in FIG. 5.

Although the holes 21 do not have regular period and pattern, when thesubstrate 10 is removed later on to expose a light emitting surface of alight emitting device, the holes 21 can increase light emittingefficiency of the light emitting device.

It is illustrated in FIG. 4 that the holes 21 have a circular shape, butthe holes 21 may be formed in a polygonal shape like a rectangle, ahexagon, etc.

Further, when the holes 21 are formed on a nitride semiconductor thinfilm layer while being aligned with regular period and pattern, aphotonic crystal structure can be formed on the light emitting surfaceby the regularly-aligned holes 21.

If the photonic crystal structure is formed, a refractive index isvaried periodically in the photonic crystal structure. When a period ofthe photonic crystal is about a half of a wavelength of the emittedlight, a photonic band gap is formed by multiple photonic scattering bya photonic crystal lattice in which the refractive index is variedperiodically.

Such a photonic crystal structure has features of effectively emittingthe light in a constant direction. Because of the photonic band gap, aphenomenon may happen that the emitted light cannot go into nor passthrough the holes 21 forming the photonic crystal structure and isextracted through portions except for the holes 21.

This phenomenon can be explained by the photon movement in the photoniccrystal structure which is formed by a plurality of holes 21 having theperiodicity.

In other words, by a plurality of holes 21 having the periodicity, thedielectric constant in the photonic crystal structure is modulatedperiodically, and light movement in the photonic crystal structure isinfluenced.

Especially, when the photonic band gap in the photonic crystal structureis included in the wavelength band of the light emitted from the lightemitting device, the photons of the light emitting device have an effectjust as being reflected from the light emitting device by a totalreflection phenomenon.

The photonic band gap has a similarity to an electron in the photoniccrystal structure, and the photons belonging to the photonic band gapcannot be propagated freely in the photonic crystal.

Accordingly, if all of the photons of the light emitted from the lightemitting device belong to the photonic band gap, all photons get out ofthe light emitting device through the portions except for the holes 21just like the total reflection phenomenon, thereby increasing the lightemitting efficiency.

In order that the photonic crystal structure effectively emits thelight, it is preferred that the depth of the holes 21, the size of theholes 21 and the distance between two adjacent holes 21 are optimizedaccording to the wavelength of the emitted light.

In the case of the nitride semiconductor light emitting device, it ispreferred that the depth of the holes 21 is set to be 0.05 to 10 μm, theradius of the holes 21 is set to be 0.01 to 6 μm, and the distancebetween two adjacent holes 21, i.e., the period of the photonic crystalis set to be 0.03 to 18 μm.

Meanwhile, together with the holes 21, it is preferable to formunit-device division regions 11 by etching, which partition the devicesfrom each other.

As shown in FIG. 6, the material having different refractive index maybe filled in the holes 21 and the unit-device division regions 11 whichare formed by etching.

It is preferable to use a dielectric material 30 like silicon dioxide(SiO₂) or silicon nitride (SiN) as the material having differentrefractive index. If the holes 21 are formed sufficiently small anddeeply, the dielectric material 30 may be not filled in the holes 21.

Also, the dielectric material 30 may be filled in at least a certainportion of the holes 21, and an n-type electrode may be formed on theregion filled with the dielectric material 30 (refer to FIG. 9).

As shown in FIG. 7, a plurality of GaN-based semiconductor layers 40 areformed on the holes 21 filled with the dielectric material 30.

The GaN-based semiconductor layers 40 include an n-type GaN layer 41, alight emitting layer (active layer) 42, and a p-type GaN layer 43. Thelight emitting layer has typically single or multiple quantum wellsstructure. At this time, in order to achieve the quantum well structure,indium (In) or aluminum (Al) may be combined with the GaN material.

As described above, by forming the division regions 11 for partitioningthe devices from each other together with the holes 21, it isunnecessary to separate the respective devices in a post-treatmentprocess after fabricating the light emitting devices.

This is because the GaN thin film is not formed on the dielectricmaterial 30 filled in the division regions 11 etched for partitioningthe devices from each other and is selectively formed only on thephotonic crystal structure (refer to FIG. 7).

Also, if selectively forming the GaN thin film on the photonic crystalstructure, the high quality n-type GaN layer 41, light emitting layer 42and p-type GaN layer 43 can be formed.

This is because the thin film layer formed selectively on the photoniccrystal structure can effectively reduce strain caused by the substrate10.

The reduction of the strain in the thin film layer has an effect ofincreasing the internal quantum efficiency of the light emitting layer42.

Further, according to the present invention, because the photoniccrystal structure includes a plurality of holes 21 and the dielectricmaterial 30 filled in the holes 21, the semiconductor layers 40 grown onthe photonic crystal structure can decrease a threading dislocationdensity, which is a defect of the thin film originating from theinterface between the substrate 10 and the semiconductor layers 40, toabout a half. The decrease of the threading dislocation density canconsiderably contribute to the improvement of the performance of thedevice.

Afterwards, as shown in FIG. 8, a material such as epoxy or the like,which can be thermochemically removed with ease, is filled in thedivision regions 11 provided between the divided devices, and a p-typeelectrode 50 is formed on the GaN-based semiconductor layers 40. Thep-type electrode forms an ohmic electrode, and a reflective electrode 60for increasing the reflection efficiency may be formed on the p-typeelectrode 50.

At this time, the timing of filling the material such as epoxy in thedivision regions 11 may be varied.

When using an oxide layer made of indium tin oxide, zinc oxide (ZnO) orthe like as the p-type electrode 50, a thin n-type GaN layer (not shown)may be additionally formed on the p-type GaN layer 43 in order toimprove the ohmic characteristics.

A support layer 70 is formed or adhered onto the p-type electrode 50 orthe reflective electrode 60, so as to function as a support plate forsupporting the overall device structure when removing the substrate 10later on.

The support layer 70 may be configured as a metal plate having a highheat dissipation effect, which is made of material selected from thegroup consisting of copper (Cu), gold (Au), nickel (Ni), and an alloythereof, or as a silicon (Si) substrate. Also, the metal plate may beformed on the reflective electrode 60 by plating.

When the metal plate is provided as the support layer 70, a seed metalmay be used for the junction between the support layer 70 and the p-typeelectrode 50 or between the support layer 70 and the reflectiveelectrode 60.

The next process is to remove the substrate 10, on which the GaNsemiconductor layers 40 are grown. In the case of the sapphire substrate10, it can be removed physically or by using laser. In the case of thesilicon substrate, it can be removed chemically or physically. It ispreferred that the surface, from which the substrate 10 is removed, issubjected to the surface treatment by etching.

At this time, as the substrate 10 is removed, the n-type GaNsemiconductor layer 20 forming the light extraction layer is exposed.Accordingly, as shown in FIG. 9, the photonic crystal structure 80including the holes 21 and the dielectric material 30 filled in theholes 21 is exposed.

In some cases, the exposed dielectric material 30 may be removed byetching.

An n-type electrode 90 is formed on the surface, from which thesubstrate 10 is removed. Even when the dielectric material 30 isremoved, it is preferable not to remove the dielectric material 30 whichis provided at the region where the n-type electrode 90 is formed.

Also, an n-type transparent ohmic layer 92 may be formed on the exposedn-type GaN semiconductor layer 20 and the holes 21, so as to improve thelight emitting efficiency by the current diffusion. The n-typetransparent ohmic layer is made of titanium/aluminum (Ti/Al) ortitanium/gold (Ti/Au), and is formed with a thickness less than aspecific value for the transparency.

Meanwhile, a reflective layer 91 may be formed beneath the n-typeelectrode 90, so that the light emitted from the light emitting layer 42is not absorbed in the n-type electrode 90 and is reflected from thereflective layer 91 to be dissipated outside.

Throughout the above-described processes, the light emitting deviceaccording to the present invention has a structure as depicted in FIG.9.

Hereinafter, the particular embodiment of the present invention will bedescribed with reference to FIGS. 3 to 9.

In this embodiment of the present invention, a metal organic chemicalvapor deposition (MOCVD) system is used for the growth of the nitridesemiconductor thin film.

Sapphire is used for the substrate 10. Ammonia is used as the nitrogensource, and hydrogen and nitrogen are used as the carrier gas.

Gallium (Ga), indium (In) and aluminum (Al) are used as the metalorganic source. Silicon (Si) is used as the n-type dopant, and magnesium(Mg) is used as the p-type dopant.

The n-type GaN semiconductor layer 20 is grown on the sapphire substrate10 to the thickness of 3 μm at the temperature of 1030° C. and thepressure of 250 Torr.

The photonic crystal period is 1.2 μm, the radius of the holes 21 is 0.4μm, and the etching depth is 3 μm. Silicon dioxide (SiO₂) as thedielectric material 30 is filled in the etched portions.

The n-type GaN layer 41 is grown on the photonic crystal structure tothe thickness of 3 μm. The light emitting layer 42 having five pairs ofmultiple quantum wells structure of indium gallium nitride/galliumnitride (InGaN/GaN) is formed on the n-type GaN layer 41.

The p-type GaN layer 43 is grown on the light emitting layer 42 to thethickness of 0.1 μm, and the n-type GaN layer is formed thinly on thep-type GaN layer 43 to improve the ohmic characteristics.

Epoxy is filled in the regions between the adjacent devices, indium tinoxide (ITO) is deposited as the p-type electrode 50 to the thickness of0.2 μm, and the reflective electrode 60 and the support layer 70 made ofcopper (Cu) are formed.

Afterwards, the sapphire substrate 10 is removed by using laser, and theexposed surface is etched by 0.5 μm to remove the crystal defect layer.

After the chemical surface-treatment on the exposed surface, the n-typeelectrode 90 is formed.

According to the experimental results of measuring the characteristicsof the light emitting device which is formed throughout the aboveprocesses and separated into the single device to be packaged, thebrightness of the device is improved by above 30%, as compared with aconventional device.

<Second Embodiment>

Hereinafter, a second embodiment of the present invention will bedescribed with reference to FIGS. 10 to 12.

In order to form a light extraction layer on a substrate, as shown inFIG. 10, a substrate 100 is subjected to surface treatment through a wettreatment process or a dry treatment process. The substrate 100 may bemade of material selected from the group consisting of sapphire, silicon(Si), zinc oxide (ZnO), silicon carbide (SiC), and a combinationthereof.

As shown in FIG. 11, a plurality of columns 200 of dielectric materialare formed on the substrate 100. The columns 200 of dielectric materialhave a cross section of a circular shape or a polygonal shape like arectangle, a hexagon, etc.

The columns 200 of dielectric material may be made of oxide or nitride,and more particularly, silicon dioxide (SiO₂) or silicon nitride (SiN).

The columns 200 of dielectric material may be formed through apatterning process or an etching process. In other words, a dielectricmaterial layer is firstly formed, and the dielectric material layer issecondarily etched to form the columns 200 of dielectric material.

The columns 200 of dielectric material may be formed on the overallregion. However, in some cases, the columns 200 of dielectric materialmay be formed only on the regions where the unit device is formed, asshown in FIG. 11. Also, in the unit-device division regions, thedielectric material may be not formed in a columnar shape, but may befilled therein (not shown). FIG. 12 illustrates the planar shape of thecolumns 200 of dielectric material which are formed only on the regionswhere the unit device is formed.

<Third Embodiment>

Hereinafter, a third embodiment of the present invention will bedescribed with reference to FIGS. 13 to 17.

As shown in FIG. 13, a GaN semiconductor thin film 110 is grown on asubstrate 100 by using a common semiconductor thin film growing device,and columns 200 of dielectric material are formed on the GaNsemiconductor thin film 110.

At this time, the GaN semiconductor thin film 110 may be formed only onthe regions where the unit device is formed. Alternatively, thesemiconductor thin film 110 may be firstly formed on the overallsurface, and a portion of the semiconductor thin film positioned on theunit-device division regions may be secondarily etched to be removed.

It is preferable to set the thickness of the thin film 110 to be 0.001to 5 μm. The thin film 110 may function as a buffer layer on thesubstrate 100.

As shown in FIG. 14, the columns 200 of dielectric material are formedon the GaN semiconductor thin film 110.

FIG. 15 illustrates the planar shape of the columns 200 of dielectricmaterial formed on the GaN semiconductor thin film 110.

Also, the columns 200 of dielectric material may be not formed in theunit-device division regions, and the dielectric material may be filledin the overall division regions.

The following processes will be described based on the structure offorming the columns 200 of dielectric material on the GaN semiconductorthin film 110. However, the following processes can also be applied to astructure of forming the columns 200 of dielectric material directly onthe substrate 100.

As shown in FIG. 16, a plurality of GaN-based semiconductor layers 300are formed on the GaN semiconductor thin film 110 on which the columns200 of dielectric material are formed.

The GaN-based semiconductor layers 300 include an n-type GaN layer 310,a light emitting layer (active layer) 320, and a p-type GaN layer 330.The light emitting layer has typically single or multiple quantum wellsstructure. At this time, in order to achieve the quantum well structure,indium (In) or aluminum (Al) may be combined with the GaN material.

At first, the n-type GaN layer 310 is not formed over the columns 200 ofdielectric material, and is formed only on the thin film 110 between thecolumns 200 of dielectric material.

If the n-type GaN layer 310 is formed on the thin film 110 between thecolumns 200 of dielectric material and covers the columns 200 ofdielectric material, the n-type GaN layer 310 is grown to form a layeras illustrated in FIG. 16.

Because the dielectric material (not shown) is filled in the unit-devicedivision regions, the GaN-based semiconductor layers 300 are not formedthereon. Therefore, it is unnecessary to separate the respective devicesin a post-treatment process after fabricating the light emittingdevices.

Also, if selectively forming the GaN-based semiconductor layers 300 onthe columns 200 of dielectric material, the high quality n-type GaNlayer 310, light emitting layer 320 and p-type GaN layer 330 can beformed.

This is because the thin film layer formed selectively on the columns200 of dielectric material can effectively reduce strain caused by thesubstrate 100.

The reduction of the strain in the thin film layer has an effect ofincreasing the internal quantum efficiency of the light emitting layer320.

Further, according to the present invention, because the columns 200 ofdielectric material are positioned beneath the n-type GaN layer 310, thesemiconductor layers 300 grown on the columns 200 of dielectric materialcan decrease a threading dislocation density, which is a defect of thethin film originating from the interface between the substrate 100 andthe semiconductor layers 300, to about a half. The decrease of thethreading dislocation density can considerably contribute to theimprovement of the performance of the device.

Afterwards, as shown in FIG. 17, a material such as epoxy or the like,which can be thermochemically removed with ease, is filled in thedivision regions provided between the divided devices, and a p-typeelectrode 400 is formed on the GaN-based semiconductor layers 300. Thep-type electrode 400 forms an ohmic electrode, and a reflectiveelectrode 500 for increasing the reflection efficiency may be formed onthe p-type electrode 400.

At this time, the timing of filling the material such as epoxy in thedivision regions may be varied.

When using an oxide layer made of indium tin oxide (ITO), zinc oxide(ZnO), aluminum zinc oxide (AlZnO), indium zinc oxide (InZnO) or thelike as the p-type electrode 400, a thin n-type GaN layer may beadditionally formed on the p-type GaN layer 330 as an ohmic-forminglayer 340 in order to improve the ohmic characteristics.

A support layer 600 is formed or adhered onto the p-type electrode 400or the reflective electrode 500, so as to support the overall devicestructure when removing the substrate 100 later on.

The support layer 600 may be configured as a metal plate having a highheat dissipation effect, which is made of material selected from thegroup consisting of copper (Cu), gold (Au), nickel (Ni), and an alloythereof, or as a semiconductor substrate like a silicon (Si) substrate.The metal plate may be formed on the reflective electrode 500 byplating.

When the metal plate is provided as the support layer 600, a seed metalmay be used for the junction between the support layer 600 and thep-type electrode 400 or between the support layer 600 and the reflectiveelectrode 500.

The next process is to remove the substrate 100, on which the GaN-basedsemiconductor layers 300 are grown. In the case of the sapphiresubstrate 100, it can be removed physically or by using laser. In thecase of the silicon substrate, it can be removed chemically orphysically. It is preferred that the surface, from which the substrate100 is removed, is subjected to the surface treatment by etching.

As the substrate 100 is removed, the columns 200 of dielectric materialarranged on the n-type GaN layer 310 of the GaN-based semiconductorlayers 300 are exposed. In some cases, the columns 200 of dielectricmaterial may be removed by etching. If the columns 200 of dielectricmaterial are removed, as shown in FIG. 18, a plurality of holes 210 areformed on the n-type GaN layer 310.

Although the columns 200 of dielectric material or the holes 210 are notarranged with the regular period and pattern, the light emittingefficiency of the light emitting device can be improved.

Meanwhile, when the columns 200 of dielectric material or the holes 210are arranged on the nitride semiconductor thin film layer with theregular period and pattern, the photonic crystal structure can be formedon the light emitting surface.

The operational effect of the photonic crystal structure is the same asthat of the aforesaid first embodiment.

The photonic crystal structure has features of effectively emitting thelight in a constant direction. In other words, because the photonic bandgap is formed, a phenomenon may happen that the emitted light cannot gointo nor pass through the columns 200 of dielectric material or theholes 210 forming the photonic crystal structure and is extractedthrough portions except for the columns 200 of dielectric material orthe holes 210.

This phenomenon can be explained by the photon movement in the photoniccrystal structure which is formed by a plurality of holes 210 having theperiodicity.

In other words, by a plurality of holes 210 having the periodicity, thedielectric constant in the photonic crystal structure is modulatedperiodically, and light movement in the photonic crystal structure isinfluenced.

Accordingly, if all of the photons of the light emitted from the lightemitting device belong to the photonic band gap, all photons get out ofthe light emitting device just like the total reflection phenomenon,thereby increasing the light emitting efficiency.

In order that the photonic crystal structure effectively emits thelight, it is preferred that the height and the radius of the columns 200of dielectric material, the distance between two adjacent columns 200,or the depth of the etched holes 210, the size of the holes 210 and thedistance between two adjacent holes 210 are optimized according to thewavelength of the emitted light.

In the case of the nitride semiconductor light emitting device, it ispreferred that the height of the columns 200 of dielectric material isset to be 0.001 to 10 μm, the radius of the columns 200 is set to be0.001 to 6 μm, and the distance between two adjacent columns 200, i.e.,the period of the photonic crystal is set to be 0.003 to 18 μm.

As a result, the depth of the holes 210, which are formed by etching thecolumns 200 of dielectric material, becomes 0.001 to 10 μm, the radiusof the holes 210 becomes 0.001 to 6 μm, and the distance between twoadjacent holes 210, i.e., the period of the photonic crystal becomes0.003 to 18 μm.

Throughout the above-described processes, the light emitting deviceaccording to the present invention has a structure as depicted in FIG.18.

Referring to FIG. 18, an n-type electrode 700 is formed on the surface,from which the substrate 100 is removed. Even when the columns 200 ofdielectric material are removed by etching, it is preferable not toremove the columns 200 of dielectric material which are provided at theregion where the n-type electrode 700 is formed.

Also, an n-type transparent ohmic layer 720 may be formed on the exposedn-type GaN layer 310 and the holes 210, so as to improve the lightemitting efficiency by the current diffusion.

Meanwhile, a reflective layer 710 may be formed beneath the n-typeelectrode 700, so that the light emitted from the light emitting layer320 is not absorbed in the n-type electrode 700 and is reflected fromthe reflective layer 710 to be dissipated outside. Additionally, ap-type contact 800 may be formed on the support layer 600 to provide alocation for electrical connection.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the inventions. Thus, itis intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A light emitting device having a vertical topology structure,comprising: a conductive support structure; a first electrode on theconductive support structure; a semiconductor structure comprising ap-type semiconductor layer on the first electrode, a light emittinglayer on the p-type semiconductor layer and an n-type semiconductorlayer on the light emitting layer; a light extraction structurecomprising a plurality of holes arranged on the n-type semiconductorlayer and a transparent layer contacting a plurality of unfilled holes,wherein the hole plurality of holes have a depth in the range of 0.3 μmto 5 μm; a second electrode on the semiconductor structure, the secondelectrode having a first width in a first direction; and a reflectivelayer located between the transparent layer and the second electrode,the reflective layer having the first width in the first direction,wherein the second electrode and the reflective layer overlap with eachother across the first width, wherein a dielectric material is formed inthe plurality of holes, the dielectric material located between thetransparent layer and the n-type semiconductor layer, and wherein thetransparent layer is disposed on an inner surface of the plurality ofunfilled holes with a thickness smaller than a radius of the pluralityof holes, and wherein the transparent layer is configured to enhancelight emission efficiency of the device.
 2. The light emitting deviceaccording to claim 1, wherein a radius of each hole of the plurality ofholes is in the range of 0.01 μm to 6 μm.
 3. The light emitting deviceaccording to claim 1, wherein the plurality of holes are periodicallydistributed.
 4. The light emitting device according to claim 3, whereinthe light extraction structure has a period in the range of 0.03 μm to18 μm.
 5. The light emitting device according to claim 3, wherein thefirst electrode comprises an ohmic electrode and a reflective electrode.6. The light emitting device according to claim 5, wherein thereflective electrode has a first surface facing the ohmic electrode anda second surface facing the conductive support structure, and wherein anarea of the second surface is larger than an area of the first surface.7. The light emitting device according to claim 1, wherein thetransparent layer comprises a transparent ohmic layer.
 8. The lightemitting device according to claim 7, wherein the transparent ohmiclayer comprises at least one of Ti, Al and Au.
 9. The light emittingdevice according to claim 1, wherein the first electrode comprisesmaterial selected from the group consisting of ITO, ZnO, A1ZnO, InZnOand a combination thereof.
 10. The light emitting device according toclaim 1, wherein the transparent layer extends outside of the pluralityof holes.
 11. The light emitting device according to claim 10, whereinthe thickness of the transparent layer outside of the plurality of holesis substantially the same as the thickness of the transparent layerdisposed on the inner surface of the pluarlity of unfilled holes. 12.The light emitting device according to claim 1, wherein the firstelectrode has a first surface facing the p-type semiconductor layer andthe p-type semiconductor layer has a second surface facing the firstelectrode, and wherein an area of the second surface is larger than thearea of the first surface.
 13. The light emitting device according toclaim 1, wherein the light extraction structure is an integral elementof the n-type semiconductor layer.
 14. The light emitting deviceaccording to claim 1, wherein the light extraction structure comprises asurface of the n-type semiconductor layer facing the second electrode.15. The light emitting device according to claim 1, wherein theconductive support structure comprises metal or semiconductor.
 16. Thelight emitting device according to claim 15, wherein the metal comprisesat least one of Cu, Au and Ni.
 17. The light emitting device accordingto claim 1, further comprising: an ohmic-forming layer on the firstelectrode.
 18. The light emitting device according to claim 17, whereinthe ohmic-forming layer comprises an n-type GaN layer.
 19. The lightemitting device according to claim 17, wherein the ohmic-forming layeris configured to improve the ohmic characteristics between the firstelectrode and the semiconductor structure.
 20. The light emitting deviceaccording to claim 1, further comprising: a metal layer between theconductive support structure and the first electrode.
 21. The lightemitting device according to claim 20, wherein the metal layer contactsthe conductive support structure.
 22. The light emitting deviceaccording to claim 20, wherein the metal layer contacts the firstelectrode.
 23. The light emitting device according to claim 1, whereinthe transparent layer contacts the second electrode.
 24. The lightemitting device according to claim 1, wherein the depth of the pluralityof holes is substantially the same as the thickness of the n-typesemiconductor layer.
 25. The light emitting device according to claim 1,wherein the thickness of the light extraction structure is substantiallythe same as the thickness of the n-type semiconductor layer.
 26. Thelight emitting device according to claim 1, wherein the transparentlayer has a substantially uniform thickness at least inside of theplurality of unfilled holes.
 27. The light emitting device according toclaim 1, wherein the light extraction structure comprises the samematerial as that of the n-type semiconductor layer.
 28. The lightemitting device according to claim 1, wherein the conductive supportstructure contacts the first electrode.
 29. The light emitting deviceaccording to claim 1, wherein the transparent layer covers an entireupper surface of the n-type semiconductor layer.
 30. The light emittingdevice according to claim 1, wherein the transparent layer isconductive.
 31. The light emitting device according to claim 1, whereinthe first electrode has a first surface facing the conductive supportstructure and the conductive support structure has a second surfacefacing the first electrode, and wherein an area of the first surface issubstantially the same as an area of the second surface.
 32. The lightemitting device according to claim 1, wherein the first electrode has afirst surface facing the semiconductor structure, and wherein a sidesurface of the semiconductor structure is substantially vertical to thefirst surface of the first electrode.